This invention relates to a method for making a molded article and, more specifically, a manifold.
Plastic air-intake manifolds for internal combustion engines have become popular due to their light weight, durability, and relatively low cost of the raw plastic material. There are currently several different processes for manufacturing plastic air-intake manifolds. One method involves injection molding a plastic manifold about a metal core insert in which the metal has a lower melting temperature than the plastic. After the manifold has been molded, the manifold is heated to a temperature sufficient to melt the core insert without melting the manifold. The metal is then captured and reused to form another core insert. This method, known as a xe2x80x9clost corexe2x80x9d method, is both expensive and labor intensive to use.
Another method involves injection molding two separate halves of a manifold which are then vibration welded together. Because the manifold is not manufactured as a single piece, there is a risk that the molded halves will separate along the welded seam or that the manifold will leak between the molded halves.
Another known method involves forming a manifold by blow molding. Flanges are added to blow molded tubular portions of the manifold by a subsequent injection molding process. Unfortunately, it is very difficult to blow mold the complex shapes required for most manifolds. Further, many manifolds require areas of varying thickness which cannot be generated with a blow molding process.
Other methods of making hollow objects out of moldable materials are known. For example, one such method involves extruding a plastic parison within a mold cavity and inflating it to form a blow molded article. Pressure is then reduced within the mold cavity to pull the blow molded article away from the mold and create a gap between the article and the mold. Next, plastic material is injected within the mold to form an injection molded layer surrounding the blow molded article. Unfortunately, if the blow molded article does not retract from the mold in a perfectly uniform manner, the final product will have an irregular inner surface and will not have a uniform thickness. Further, a thin walled blow molded article could collapse or disintegrate when contacted by high temperature, high pressure injection molded material.
What is needed is an improved method of forming a plastic article such as an intake manifold that provides the benefits of injection molding to create smooth, complex surfaces without requiring an expensive xe2x80x9clost corexe2x80x9d method of operation.
The present invention provides a method of manufacturing a molded article. The method includes inflating a blow moldable article within an interior cavity of a first mold to form a blow molded article having an outer surface, inserting the blow molded article within an interior cavity of a second mold which substantially envelops the blow molded article and is larger than the interior cavity of the first mold, and injecting moldable fluid material within the interior cavity of the second mold adjacent the outer surface of the blow molded article. During the injecting step, sufficient pressure is applied within the blow molded article to substantially maintain the shape of the blow molded article against the inwardly directed force of the moldable fluid material injected into the mold.
The present invention also provides a method of manufacturing a molded article comprising the steps of inflating a blow moldable article to form a blow molded article having an outer surface, inserting the blow molded article within an interior cavity of a mold, and inserting moldable fluid material within the interior cavity of the mold adjacent the outer surface of the blow molded article. While the moldable fluid material is being inserted, cooling fluid is applied within the blow molded article at a temperature sufficient to maintain the shape of the blow molded article. The temperature of the cooling fluid is selected based on the melting temperature of the blow molded article and the heat transfer from the moldable fluid material to prevent the blow molded article from losing structural integrity due to heat transfer from the moldable fluid material.
The present invention also provides a method of manufacturing a multi-layered manifold comprising the steps of inflating a blow moldable article within an interior cavity of a first mold to form a blow molded inner layer of the manifold, inserting the blow molded inner layer within an interior cavity of a second mold which substantially envelops the blow molded inner layer and is larger than the interior cavity of the first mold, and injecting moldable fluid material within the interior cavity of the second mold to form an outer layer of the manifold which substantially surrounds the blow molded inner layer. During the injecting step, pressure is maintained within the blow molded inner layer to substantially maintain the shape of the blow molded inner layer
The present invention also provides a molded article including a blow molded inner core formed by inflating a blow moldable article within an interior cavity of a first mold. The article also includes an injection molded outer layer formed by inserting the inner core within a second mold having an interior cavity larger than the interior cavity of the first mold, injecting moldable fluid material within the second mold to substantially envelop the inner core, and maintaining pressure within the blow molded inner core sufficient to substantially maintain the shape of the blow molded inner core.
With the present invention, a blow molded article can be inexpensively formed and then used as an insert during an injection molding process. By applying pressure within the blow molded insert during injection molding, the integrity of the blow molded insert is maintained. Thus, the present invention provides the benefits of injection molding without requiring either a xe2x80x9clost corexe2x80x9d method or a method in which the final product is formed in sections which must be welded together.
Further, the use of a temperature-controlled fluid within the blow molded insert while the outer layer is formed prevents deterioration of the structural integrity of the insert resulting from heat transfer from the high temperature molding fluid used to form the outer layer.